Apparatus of this kind has become known from DE-OS 27 00 003. This known apparatus serves for the production of strand profiles from plastic materials. In the screw extruder of this apparatus the plastic material is melted, then passed through a strainer in order to remove any foreign particles from the molten plastic material whereupon the molten and strained plastic material is led to a gear pump which imparts to the molten plastic material sufficient pressure to force it through an extrusion head secured on the outlet of the gear pump and thereby extrude the desired profile. The advantage of using a gear pump in the extrusion installation is that a very uniform pressure can be produced for the extrusion of the material from the extrusion head. A further advantage of the gear pump in such extrusion installation is that the screw of the extruder can be shorter than usual because the screw serves only for disintegration of the plastic material to a low viscosity homogenous mass and is not required to build up the pressure necessary for the extrusion from the extrusion head. The extrusion installation can hence be made shorter than the usual screw extruder of which the screw serves not only for the disintegration work but also for the work of building up the extrusion pressure. This advantage is not realized by DE-OS 27 00 003 where the construction units are arranged in a straight production line far apart from one another so that a considerable amount of room is needed.
With this known extrusion installation the axes of the gear wheels of the gear pump are arranged perpendicular to (and offset from) the axis of the screw of the extruder. This arrangement is also usual in screw extruder and gear pump extrusion installations for plastic material.
Such extrusion installations consisting of a screw extruder and gear pump have not heretofore been employed in working with rubber mixtures. Rubber mixtures plasticized in a screw extruder exhibit different molecular structure from molten plastic material. They erode gear pumps by reason of their abrasive character and can lead to break downs.
Recent special knowledge attributes this fault to the fact that the strand of the plasticized rubber mixture led into the gear pump leads to damage of the gear pump by its molecular alignment. This knowledge suggests that damage to the gear pump can be avoided by arranging the gear pump directly behind the tip of the screw of the screw extruder so that a gear pump receives from the extruder a plasticized rubber mixture which has not yet been formed into a strand. This arrangement leads also to a very short type of construction of the extruder installation.